The use of the full SIF spectrum in combination with the optical domain as indicators of photosynthesis and plant productivity has still not been fully exploited. For two years, FLUOPHOT focussed on this knowledge gap, and specifically on the remote observation of the photoprotection mechanisms at the leaf level. This information is required to obtain a better link between the sun-induced fluorescence and the actual photosynthesis of vegetation. In absence of physiological stress and under non-saturating light conditions, a more direct (linear) link between photochemistry and SIF emission might be established. However, in contrast, when stress occurs, photoprotection mechanisms are activated and controlled heat dissipation or non-photochemical energy quenching (NPQ) becomes more competitive in the energy dissipation balance. Thus, in order to establish the link between SIF and photosynthesis unambiguously, simultaneous measurements of the controlled energy dissipation mechanisms are needed. The in-depth identification and description of specific spectral contiguous signatures linked to the various photoprotection mechanisms are still poorly understood, especially from a proximal or remote sensing point of view.
During the project, hyperspectral datasets at both the leaf and the canopy level were collected for several plant species, while monitoring the dynamical fluorescence and photoprotection mechanism during adaptation to high light intensity. In this way, the dynamical hyperspectral responses to plant physiological processes were assessed and interpreted.
Based on this experimental work, novel insights on the spectral behaviour of vegetation linked to the physiological processes were revealed. The in vivo occurrence of both quick and slowly activated photoprotection mechanisms could be identified from the optical data. The absorbance shifts in the range 500-780 nm are found to be strong and related to the organizational changes of the photosynthetic apparatus. With this, FLUOPHOT brought first insights in the remote observation of plant photoprotection, which is manifested over a wide spectral range of the optical domain. These findings might pave a way towards a further non-invasive spectral investigation of the non-photochemical energy quenching (NPQ) mechanisms, which is, in combination with F measurements, of a high importance for assessing plant photosynthesis in vivo and in addition from remote observations.
